The present invention relates to hearing devices. More specifically, the present invention relates to hearing devices that are worn entirely in the ear canal for extended wear without daily insertion and removal as required with conventional hearing aids.
The external acoustic meatus (ear canal) is generally narrow and contoured as shown in the coronal view in FIG. 1. The ear canal 10 is axially approximately 25 mm in length from the canal aperture 15 to the tympanic membrane or eardrum 18. The lateral part, the part away from the tympanic membrane, of the ear canal comprises a cartilaginous region 11. Cartilaginous region 11 is relatively soft due to the underlying cartilaginous tissue. Cartilaginous region 11 of the ear canal 10 deforms and moves in response to the mandibular or jaw motions, which occur during talking, yawning, eating, etc. The medial part, the part toward the tympanic membrane, comprises a bony region 12. Bony region 12 is proximal to the tympanic membrane and is rigid. Bony region 12 or the “bony canal” is roughly 15 mm long, representing approximately 60% of the canal length. The skin in the bony region 12 is thin relative to the skin in the cartilaginous region and thus more sensitive to touch or pressure. There is a characteristic bend that occurs approximately at the bony-cartilaginous junction 17, which separates cartilaginous region 11 and from bony region 12.
Hair 5 and debris 3 in the ear canal are primarily present in the cartilaginous region 11. Physiologic debris includes cerumen or earwax, sweat, decayed hair, and oils produced by the various glands underneath the skin in the cartilaginous region. Non-physiologic debris is also present and may consist of environmental particles, including hygienic and cosmetic products, that may have entered the ear canal. Canal debris is naturally extruded to the outside of the ear by the process of lateral epithelial cell migration, offering a natural self-cleansing mechanism for the ear.
The ear canal 10 terminates medially with the tympanic membrane 18. Lateral of and external to the ear canal is the concha cavity 2 and the auricle 4, which is cartilaginous. The junction between the concha cavity 2 and cartilaginous region 11 of the ear canal at the aperture 15 is also defined by a characteristic bend 7, which is known as the first bend of the ear canal. Canal shape and dimensions can vary significantly among individuals.
When compared to cartilaginous region 11, bony region 12 is dimensionally more stable since the underlying tissue is osseous and also physiologically less active due to the absence of hair, cerumen or sweat glands, present only in the cartilaginous portion.
Extended wear hearing devices, such as those described in U.S. Pat. No. 7,215,789 to Shennib et al., U.S. Pat. No. 6,940,988 to Shennib et al., U.S. Pat. No. 6,473,513 also to Shennib et al., are worn continuously from several weeks to several months inside the ear canal. These devices, as taught by Shennib et al., may be miniature in size in order to fit entirely within the ear canal and are adapted for the receiver to fit deeply in the ear canal in proximity to the tympanic membrane (TM). However, the devices as taught may extend into the cartilaginous portion of the ear canal.
An optimized placement for these devices is entirely in the bony part of the ear canal, avoiding placement in the cartilaginous portion of the ear canal. Placement in this manner may be desirable for many reasons including: (1) stability—because the bony part is immobile and the cartilaginous part is subject to movements and deformations, which can interfere with the hearing device by moving it or dislodging it from its intended position; (2) comfort of wear—canal interference with the hearing device can cause discomfort, irritation and even laceration of the ear canal; and (3) device longevity—because physiological debris is present primarily in the cartilaginous part of the ear canal, placement of the device in the bony canal can reduce the probability of contamination by debris in the canal.
In order to avoid placement of the device in the cartilaginous area of the ear canal, the hearing device should be made sufficiently short to fit only in the bony part between the junction 17 and the tympanic membrane 18. Therefore, the hearing device should be considerably shorter than 15 mm to fit most individuals in the bony region only and allowing for safe distance from the tympanic membrane. Many hearing devices, including the extended wear devices mentioned above, are too long and do not fit entirely in the bony canal. Many inventions provide various methods for dealing with partial placement in the cartilaginous part of the ear canal. These methods include the suspension of a lateral assembly and articulation of the device as will be discussed in more details below.
Hearing aid receiver (referred to here alternatively as speakers) may be highly miniaturized but sufficiently sized to efficiently produce amplified sound to the tympanic membrane. These speakers are generally in the shape of a rectangular prism with lengths in the range of 5-7 mm and 2-3 mm in girth at the narrowest dimension. These speakers confer substantial length to the hearing device. Smaller dimensions are possible to manufacture but generally lead to undesirable reduction in output efficiency and are thus not currently commercially available. The reduction in output efficiency may not be acceptable for hearing aid manufacturers since the output efficiency reduction may necessitate increasing the power consumption significantly to produce the required amplification level for a hearing impaired individual. Examples of miniature hearing aid speakers include FH and FK series receivers made by Knowles Electronics and series 2600 made by Sonion (Denmark).
Miniature microphones for hearing aids also exist with form factors that confer length or bulk to the miniature hearing devices. These miniature microphones are generally in rectangular prism shape or in cylindrical shape, ranging from 2.5-5 in length to 1.3- to 2.6 mm in the narrowest dimension. Examples of miniature microphone include FG and TO series by Knowles Electronics, series 6000 by Sonion, and series 151 by Tibbetts Industries. Electret type microphones are widely used in hearing aids for their superior sensitivity, low noise characteristics and wide dynamic range. Electret type microphones can also have good vibration rejection characteristics for minimizing the effects of speaker or shell-conducted vibrations. Silicon microphones, not yet widely used, promise improved miniaturization and reduced vibration sensitivity. Similarly, smaller microphones can be manufactured but generally at the expense of reduced sensitivity and increased noise levels. Resorting to smaller microphone with inferior specifications is seldom acceptable by hearing impaired users who demand improved sound fidelity.
In canal hearing aid devices, conventional and extended wear types, the transducers (speaker and microphone) are positioned with extreme care with respect to one another to minimize the occurrence of internal and external “feedback” generation. Feedback is the unwanted whistling in a hearing device due to the coupling between the microphone and receiver. Basically, feedback occurs when a portion of the output energy from the receiver reaches the microphone and causes a self-sustained oscillation. Causes and mitigation of feedback in hearing devices are discussed in more details in columns 9 and 10 of U.S. Pat. No. 5,701,348, the contents of which are fully incorporated herein by reference. The opportunity for feedback is directly proportional to the acoustic gain (volume) and may thus be more likely to occur in hearing devices for persons with significant hearing losses. Feedback is also more likely to occur as the device gets smaller due to the reduction of the distance and increased coupling between the transducers.
To minimize feedback in miniature canal hearing devices, the speaker and the microphone can be placed with maximum axial spatial separation to minimize sound and vibration cross coupling. For example, in FIGS. 3-5 of commonly owned U.S. Pat. No. 6,940,988 and FIGS. 3 and 5 of commonly owned U.S. Pat. No. 7,215,789, the speaker or receiver is placed most medially toward the tympanic membrane and the microphone is placed most laterally toward the aperture 15 of the ear canal. By maximizing the axial spatial separation between the speaker and the microphone, higher feedback-free amplification levels can be achieved. Another method used in hearing devices to minimize feedback is the use of damping material to suspend or isolate the microphone and the speaker within the housing of the device, for example, by using viscoelastic material to encapsulate vibration sensitive components or by filling the space within the hearing device as described in U.S. Pat. No. 4,969,534, the contents of which are fully incorporated herein by reference. However, even with the use of optimal damping material and techniques, maximum spatial separation between the transducers is often necessary for the mitigation of feedback. This separation requirement may result in hearing devices considerably longer than 12 mm when considering other components needed to operate the device such as battery, amplifiers, electronic circuits, mounting parts, etc. Lengths in excess of 12 mm may be acceptable for a user-inserted hearing devices which may also be referred to here as daily wear devices. However, for extended wear canal hearing devices designed to operate continuously in the ear canal for up to several months, lengths exceeding 12 mm will often place the device partially in the cartilaginous portion of the ear canal when considering the need for approximately 3 mm of safety gap between the device and the tympanic membrane.
In prior hearing devices, such as those described in FIG. 4 of commonly owned U.S. Pat. No. 6,940,988 and FIG. 5 of commonly owned U.S. Pat. No. 6,473,513, mitigation of canal interference may be accomplished by suspending (in a non-contact or minimum contact fashion) the lateral assembly within the cartilaginous canal. The suspension may provide clearance for the device most of the time but occasionally the user may experience transient interference, for example, during yawing or sleeping on the ear, which may lead to device movement and in some cases discomfort. A transient interference can cause irritation of the skin in the bony canal, which is extremely sensitive to touch and movements. Large device movements due to canal deformations can also lead to dislodgment of the device from its intended position. Interference and device movements usually necessitate the untimely removal of the device from the ear canal prior to device end of life.
To facilitate the insertion of an extended wear device and to mitigate the effects of canal deformations, prior extended wear devices may use articulated assemblies with flexibly joints, for example, flexible connection 79 in commonly owned U.S. Pat. No. 7,215,789. This articulation can allow the lateral assembly to move in response to canal deformations or due to accumulation of debris in the cartilaginous portion. However, this articulation often adds length, cost and complexity to the manufacturing process of the device.
It is the objective of this invention to provide a shorter hearing device that fits entirely in the bony part of the ear canal for improved comfort, stability and durability.
Another objective is to provide an extended wear canal device which is not susceptible to canal movements and deformation present in the cartilaginous canal.
Another objective of this invention is to provide a hearing device that is 12 mm or less in length for fitting substantially in the bony part of the ear canal past the bony-cartilaginous junction when inserted within.
Yet, another objective of this invention is to provide an arrangement for an extended wear canal device without articulation for improved cost and reliability and shorter length.